In recent years, since ink-jet recording systems enable simple image formation at low cost, they have been applied to various printing fields such as photography, various types of printing, marking, and special printing such as color filters.
Ink-jet inks, employed in the above ink-jet recording systems, include a plurality of inks such as a water-based ink which employs water and a small quantity of an organic solvent, a non-water-based ink which employs an organic solvent and substantially does not employ water, a hot-melt ink which is solid at room temperature and is applied to printing while heated and molten, and an actinic radiation curable ink which is cured via actinic radiation such as light, and each of them is appropriately selected depending on the intended application.
In recent years, there have been developed ink-jet inks for industrial use which can be printed directly on a non-absorptive recording medium such as a polyvinylchloride sheet. Examples of these ink-jet inks are cited as: a solvent ink in which an organic solvent is used as a vehicle of an ink; and a UV ink containing a polymerizable monomer as a primary component of an ink. A solvent ink is dried by evaporating its solvent to the air, as a result, a solvent ink has a problem of emitting a large amount of VOC (Volatile Organic Compound), which becomes a social problem in recent years. There are other concerns for a worker about an odor or an effect for the safety. Therefore, it is required to provide equipment for making sufficient ventilation. A UV ink is made harden immediately after printing, therefore, an emission of VOC is close to zero, but many monomers to be used in the ink may have problem of skin sensitization. Moreover, there are requirement of incorporating an expensive UV light source into a printer, and it cannot be used for printers for every field.
In the above-described background, there has been developed an ink which can be printed also directly to a non-water absorptive recording medium, by using a water-based ink containing water as a major component which has been widely used in homes and has reduced effects on the environment.
There has been proposed a water-based ink containing a water miscible solvent selected from glycols and glycol ethers. Moreover, there has been proposed an ink containing a graft co-polymer binder which contains a hydrophobic backbone and a non-ionic and hydrophilic side-chain, wherein the graft co-polymer binder is soluble in a water-based vehicle and is not soluble in water (for example, refer to Patent Document 1).
Disclosed was a water-based pigment ink in which an ink was heat-fixed against a recording medium of vinyl film or coated by vinyl resin by employing an ink soluble resin (for example, refer to Patent Documents 2 and 3).
Further, there has been proposed a plurality of water-based inks which employs insoluble resin particles into an ink as a binder resin (for example, refer to Patent Documents 4 to 7).
However, these inks disclosed in Patent Documents were insufficient to obtain an image texture depending on species of a recording medium, and ejection stability, the recovery property after a nozzle clogging, or a storage stability of an ink was not fully satisfactory.
Further, when a binder resin was added to a water-based printing ink or a water-based inkjet ink so as to enhance durability of recorded image film, the image film caused to become white during drying process, resulting in extremely lowering gloss of an image, depending on species of pigment dispersant or solvent in an ink. This whitening phenomenon causes extreme damage to an image quality specifically in a non- (or slight-) absorptive recording medium such as glossy film or printing paper.
Thus, it is desired to develop an ink which can resolve all of a whitening of the recorded image film, loosing an image texture on some recording medium, ejection stability or a recovery property after a nozzle clogging, or a storage stability of an ink.